Silica has long been used as a reinforcing filler in tread compounds, as a partial or total substitute for carbon black, because of the advantages it affords in terms of rolling resistance and wet road-holding performance.
Silica is used in conjunction with silane bonding agents, which, bonding with silanol groups, prevent the formation of hydrogen bonds between silica particles and, at the same time, bond the silica chemically to the polymer base.
Trialkoxymercaptoalkyl-silanes are a particularly interesting class of silane bonding agents, especially in terms of the advantages they afford in reducing both rolling resistance and the emission of volatile substances.
The most advantageous is the compound of formula I below.SH(CH2)3SiR1R22  (I)
where:
R1 is —OCH2CH3 and
R2 is —O(CH2CH2O)5(CH2)12CH3
Despite the advantages referred to above, however, this class of silane bonding agents produces an increase in the viscosity of the compound and, hence, processing problems.
To solve the processing problems involved, plasticizing oils are normally added to the compound, but this has the effect of producing additional problems by impairing the physical characteristics, such as wear resistance, of the compound.
A need is therefore felt for a method of producing rubber tyre compounds, which allows the use of silane bonding agents in the trialkoxymercaptoalkyl-silane class, but without incurring processing problems and/or impairing the physical characteristics of the compound.